JP2980706B2 - Projection display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection display device which projects an optical image formed on a light valve on a screen by irradiating the optical image with irradiation light.

[0002]

2. Description of the Related Art In order to display an image on a large screen, an optical image corresponding to an image signal is formed on a relatively small light valve as a change in optical characteristics, and this optical image is irradiated with illumination light, and is projected by a projection lens. 2. Description of the Related Art A projection display device that enlarges and projects an image on a screen is conventionally known. As a light valve, a liquid crystal panel in which pixels are arranged in a matrix has recently been used. As a rear projection type screen, a two-panel screen using a combination of a Fresnel lens and a lenticular lens is generally used.

FIG. 11 shows a configuration of a rear projection type display device using two rear projection type screens.
A light valve 2 composed of a liquid crystal panel is illuminated by an illumination system 1, and its optical image is enlarged by a projection lens 3 and formed on a surface of a two-screen 6 composed of a Fresnel lens 4 and a lenticular lens 5. Fresnel lens 4
Causes the incident light to be directed substantially in the direction in which the observer is located, and the lenticular lens 5 disperses the light emitted from the Fresnel lens 4 in appropriate horizontal and vertical angles at an appropriate distribution ratio.

If the pixels of the light valve 2 are arranged in a matrix, the image enlarged and formed on the screen 6 forms a matrix of pixels. When both the lens 5 and the lens 5 have a periodic structure in the horizontal direction, a moiré whose density changes in the horizontal direction is generated. The presence of this moiré makes it difficult to see the projected image on the screen. Therefore, there have been proposed several devices for making the moiré less noticeable. Pixel pitch of 1/2 or less, and in Japanese Patent Application Laid-Open No. 2-79991, they are 1/5 and 1 / 2.5.

[0005]

As proposed in the above patent publication, specifying the ratio between the pitch of the lenticular lens and the pixel pitch of the projected image is an effective technique for reducing moire. . Also, it is known that the smaller the pitch of the lenticular lens and the smaller the pitch ratio, the less noticeable the moiré becomes.

Meanwhile, among the lenticular lenses currently used, those having a small color shift and a high contrast have lenses formed on both the front surface and the back surface as shown in FIG. As the pitch becomes finer, it is necessary to make the lens thinner. As a result, there is a problem that the lens is liable to be broken, handling and setting become difficult, and the manufacturing cost is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a projection display device capable of reducing moire without reducing the pitch of a lenticular lens as compared with the related art. .

[0008]

Means for Solving the Problems The present inventors made a theoretical study of moire and found that the above object can be achieved.

According to the present invention, the pixel period of a projected image in a direction having a periodic structure of a screen is provided between a light valve having pixels arranged in a matrix and a screen for projecting an optical image of the light valve. An optical element for selectively attenuating a spatial frequency component that is an integral multiple of the corresponding spatial frequency is provided.

In the case of a projection type device using a screen having a periodic structure in the horizontal and vertical directions, a similar optical element may be provided between the screen and the light valve.

[0011]

By providing an optical element between the screen and the light valve, a spatial frequency component that is an integral multiple of the spatial frequency corresponding to the pixel period of the projected image causing moire in the projected image projected on the screen is reduced. Will be reduced.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments, the results of theoretical elucidation of moire will be described. FIG. 1 shows an optical model diagram of a light valve having pixels arranged in a matrix. That is, the optical apertures 8 having image information are arranged in a matrix in the optical apertures 9. When the light valve is a liquid crystal panel, the ratio of the opening 8 generally decreases as the pixel pitch on the liquid crystal panel becomes smaller. The direction corresponding to the horizontal direction at the time of projection is taken on the x-axis, the entire white image is input and illuminated, and the light intensity I (x) on the line AA ′ when projected on the screen surface is calculated. It is shown in FIG. On the other hand, of the light incident on a lenticular lens having a periodic structure in the horizontal direction, the light intensity T transmitted substantially in front of the projection display device is shown.
(X) is shown in FIG. The ratio of the light transmitted obliquely in the horizontal direction is shifted from the phase shown in FIG. Here, P _L and P _LB represent a lenticular pitch and a light valve pixel pitch on a screen, respectively.

When the shapes shown in FIGS. 2A and 2B are converted into mathematical expressions, the following is obtained.

(Equation 1)

(Equation 2) Therefore, when a white image is input as a whole, the intensity of light transmitted substantially in front of the display device is the product of Equations 1 and 2, and is as follows.

(Equation 3) In Equation 3, the second term has a finer period than the pitch of the lenticular lens, so there is no problem on the image, but the first term is moiré. Therefore, for each of n and m,

(Equation 4) Is required to reduce moire as much as possible.

Here, in the prior art, I (x)
And the change in T (x) in the x direction was close to a rectangle,
Harmonic component is large, n of n ≧ 2, m ≧ 2, it is necessary to reduce the value of the number 4 also m, had to reduce the pitch P _L of the lenticular lenses. By the present invention to minimize the _{a n (n ≧ 2),} n of n ≧ 2, m ≧ 2, also reduce the value of the number 4 for m, without decreasing the pitch P _L of the lenticular lenses It reduces moire.

Next, a means for reducing a _n (n ≧ 2) will be described.

FIGS. 3, 4 and 5 show different configurations of the projection display device according to the present invention. In the figure, FIG.
The same reference numerals indicate the same components.

In any configuration, a spatial frequency component (a ₁ ) corresponding to the pixel period of the projected image or a spatial frequency component (a _n ) (n ≧ _n ) that is an integral multiple of the spatial frequency is used.
An optical low-pass filter 7 designed to selectively attenuate 2) is inserted. When a low-pass filter is used, generally, there is a tendency that frequencies lower than the frequency to be selectively attenuated tend to be attenuated. Therefore, when it is necessary to prevent a decrease in image resolution, a _n (n ≧ n)
It is better to selectively attenuate 2). FIG. 2 shows a change in light intensity on the screen surface when a low-pass filter is inserted by a broken line.

As the optical low-pass filter used, there are a filter utilizing birefringence of quartz and a filter utilizing a diffraction grating.

If the screen has a periodic structure also in the vertical direction, the above concept may be applied in the vertical direction.

Hereinafter, the present invention will be described specifically with reference to examples. In the following embodiments, a low-pass filter using a diffraction grating is used.

FIG. 3 shows an embodiment of the present invention. In FIG. 3, a diffraction grating is provided between the projection lens 3 and the screen 6 as an optical low-pass filter 7.

Here, the effect of the diffraction grating as an optical low-pass filter will be described. FIG. 6 shows a diffraction grating having a rectangular wave shape, and its MTF (Modulation Transfer Functio) is shown.
n) The characteristics are shown in FIG. The period of the diffraction grating 7 d, and the width of the grid of the convex portion 7a a, the distance between the grid 7 and the screen 6 b, the wavelength of the incident light and lambda, the cut-off frequency f _a and f _b of FIG. 8 , 0 <a ≦ d / 2, are represented by the following Expressions 5 and 6, respectively.

F _a = a / bλ

F _b = (d−a) / bλ Also, when d / 2 <a <d, it is expressed by the following equations 7 and 8.

[Mathematical formula-see original document] f _a = (da) / bλ

[Equation 8] f _b = a / bλ

Therefore, if the distance b between the optical low-pass filter 7 and the screen 6 is determined, the period d of the diffraction grating 7 and the width a of the projection 7a in FIG. 6 are optimized, and the cutoff frequency 1 / P _{LB is obtained.} Or an integer multiple of spatial frequency n / P _LB
Is set to, can be number 4 of a _n is reduced, to reduce moire. Also, the cutoff frequencies f _a and f _b
If wide width, it is possible to reduce a plurality of a _n, it is possible to further reduce the moire.

In order to reduce moire in two directions, that is, a horizontal direction and a vertical direction, a diffraction grating having gratings in two directions as shown in FIG. 9 may be used.

Embodiment 1 Assuming that the horizontal pixel pitch P _LBH of the projected image of the light valve 2 on the screen 6 in FIG. 1 is 1.29 mm, the optical low-pass filter 7 operates at a spatial frequency corresponding to the pixel pitch P _LBH. It is necessary to attenuate a spatial frequency of 0.77 lines / mm or an integral multiple of 0.77 × n _H lines / mm. When the distance between the low-pass filter and the screen 6 is 1900 mm, the period d of the diffraction grating in FIG. 6 is 2.43 mm, the width a of the projection is 0.81 mm, and the phase difference σ between the projection and the recess is 2π.
/ 3, the MTF characteristic as shown in FIG.
Since 77 lines / mm and 1.55 lines / mm can be attenuated, moire in the horizontal direction can be reduced.

Embodiment 2 Assuming that the horizontal pixel pitch P _LBH of the projected image of the light valve 2 on the screen 6 in FIG. 1 is 1.29 mm and the vertical pixel pitch P _LBH is 0.968 mm, an optical low-pass In the horizontal direction, the filter 7 needs to attenuate a spatial frequency of 0.77 lines / mm corresponding to the pixel pitch P _LBH , or an integer multiple of a spatial frequency of 0.77 × n _H lines / mm. Further, in the vertical direction, it is necessary to attenuate the spatial frequency web 1.03 lines / mm corresponding to the pixel pitch P _LBV or a spatial frequency 1.03 × n _V lines / mm which is an integral multiple.
The distance between the low-pass filter 7 and the screen 6 is 1900
mm, the period d ₁ of the diffraction grating in FIG. 9 is 1.62.
mm, the width a _{1 of the} convex portion is 0.81 mm, and the period d ₂ is 2.15 m.
m, when the a ₂ of protrusions 1.08 mm, also the phase difference σ between the raised portion and the depressed portion and [pi, MTF as shown in FIG. 10 (a), (b)
Characteristics can be obtained, and 0.77 lines / mm in the horizontal direction and 1.03 lines / mm in the vertical direction can be attenuated. Therefore, moire in both the horizontal direction and the vertical direction can be reduced.

In this embodiment, the optical low-pass filter 7
Is arranged between the projection lens 3 and the screen 6, but is arranged between the light valve 2 and the projection lens 3 as shown in FIG. 4 or at a position close to the screen 6 as shown in FIG. Can obtain the same effect. Further, in this embodiment, the cross-sectional shape of the diffraction grating is rectangular as shown in FIGS. 6 and 9, but may be a sine wave or trapezoidal wave.

[0028]

According to the projection display of the present invention, moire can be reduced without reducing the pitch of the lenticular lens. As a result, since it is not necessary to make the lenticular lens thin, the handling and setting are easy without reducing the strength, and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 shows an optical model of a light valve having a matrix of pixels.

FIG. 2 is a diagram showing a change in light intensity on a screen and a light transmittance of a lenticular lens.

FIG. 3 is a configuration diagram of an embodiment of a projection display device according to the present invention.

FIG. 4 is a configuration diagram of another embodiment of the projection display apparatus according to the present invention.

FIG. 5 is a configuration diagram of still another embodiment of the projection display apparatus according to the present invention.

FIG. 6 is a perspective view of an example of a diffraction grating used as an optical low-pass filter in the projection display according to the present invention;

FIG. 7 is an MTF characteristic diagram of the diffraction grating shown in FIG.

8 is an MTF characteristic diagram of the diffraction grating shown in FIG.

FIG. 9 is a perspective view of another example of an analysis grating used as an optical low-pass filter in the projection display according to the present invention;

10 is an MTF characteristic diagram of the diffraction grating shown in FIG.

FIG. 11 is a configuration diagram of an example of a conventional projection display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Illumination system 2 Light valve 3 Projection lens 4 Fresnel lens 5 Lenticular lens 6 Screen 7 Low-pass filter 8 Optical opening of light valve 9 Optical opening of light valve

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-311887 (JP, A) JP-A-50-93146 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 27/46 G03B 21/00 505 G02F 1/13

Claims (2)

(57) [Claims] 1. A screen having a periodic structure in one direction, a light valve having pixels arranged in a matrix, a light source for irradiating the light valve, and an output light from the light valve. In a projection display device including a lens that projects an optical image onto the screen, a spatial frequency corresponding to a pixel period of a projected image in a direction having a periodic structure of a screen between the light valve and the screen. A projection type display device provided with an optical element for selectively attenuating a spatial frequency component that is an integral multiple of two or more of the following . 2. A screen having a periodic structure in a horizontal direction and a vertical direction, a light valve having pixels arranged in a matrix, a light source for irradiating the light valve, and receiving output light from the light valve. In a projection display device including a lens for projecting an optical image of a light valve onto the screen, between the light valve and the screen, a horizontal spatial frequency corresponding to a pixel period of a horizontally projected image is provided. and 2 or more integer multiples of the horizontal spatial frequency components, the optical element for selectively attenuating at least one of the two or more integral multiple of the vertical spatial frequency components in the vertical spatial frequency corresponding to the period of pixels in the vertical direction of the projected image A projection display device, comprising: